92 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
PL XI, A), and of the Magnet lode. The quartz in this case has often 
grown radially outward from kernels of tetrahedr'ite. Less conspicu- 
ous radial structure was noted in the Silver Queen, at the head of 
Placer Gulch. 
MICROSCOPICAL FEATURES. 
In the larger lodes, with massive structure, particularly those carry- 
ing much galena, the crystallization is, as a rule, so coarse that 
microscopical study is of use only in furnishing details of mineralog- 
ical structure/ The quartz of such lodes shows the usual character 
of vein quartz, and has crystallized in large, irregular grains, inter- 
locking with one another and with the principal ore constituents. The 
structure, when sufficiently fine to be embraced in a thin section, 
is typically hypidiomorphic granular (PL IX). Microscopic fluid 
inclusions with gaseous bubbles, often arranged along curved sur- 
faces within the quartz, are always present. No special investigation 
of the hermetically inclosed liquids of these minute cavities has been 
made for this region, but they are probably solutions of calcium and 
alkaline sulphates, with some chlorides, and ver} r likely carbonic acid. 1 
Interstitial or miarolitic cavities into which the quartz crystals some- 
times project are common, and are often filled with calcite, or, in the 
Silver Lake Basin, with chlorite (PL IX, .4). 
Vein quartz varies widely in the size of the constituent crystal 
grains. In the Sunnj'side and neighboring lodes the galena, sphal- 
erite, and chalcopyrite are distributed through the gangue in smaller 
particles, and the quartz grains themselves are correspondingly smaller 
than those in the Silver Lake veins. PL IX, B, shows a typical thin 
section of Sunnyside ore, in which chalcopyrite and sphalerite happen 
to be the dominant ore minerals. 
Still other ores, of which that of the Ridgway mine may be taken 
as a type, exhibit throughout much finer crystallization. The quartz 
occurs in small interlocking grains, and the ore particles, which in 
hand specimens are often so small as to render the quartz cloudy or 
black, without ' being themselves individually noticeable, are seen 
under the microscope to be thickly sprinkled through the gangue 
and to be very irregular in shape. They occur both in the sutures 
between the quartz grains and within the grains themselves (PI. 
X, A). Such ore is almost invariably said by the miners to contain 
brittle silver. But neither chemical tests nor the microscope reveal 
stephanite. In the Ridgway ore the particles are chiefly argentite witq 
some pyrite, a little sphalerite, and sometimes a little galena. These 
finely crystalline ores are worked for silver and gold, as the galena is 
rarely abundant enough to pay for extraction. But they are by no 
means equally rich. In some cases the finely disseminated ore parti! 
1 Gold-quartz veins of Nevada City and Grass Valley districts, by Waldemar Lindgren: Seven- 
teenth Ann. Rept. U. S. Geol. Survey, LS96, Pt. II, p. 131. 
